A book cipher is a cipher in which each word or letter in the plaintext of a message is replaced by some code that locates it in another text, the key.
The King James Bible, a highly available publication suitable for the book cipher.
In cryptography, a substitution cipher is a method of encrypting in which units of plaintext are replaced with the ciphertext, in a defined manner, with the help of a key; the "units" may be single letters, pairs of letters, triplets of letters, mixtures of the above, and so forth. The receiver deciphers the text by performing the inverse substitution process to extract the original message.
The forged nomenclator message used in the Babington Plot
A French nomenclator code table
Enigma cipher machine as used by the German military in World War II